Actuation units for immersion pumps currently comprise an electric motor which is associated in a lower region with the pump and is closed in a hermetic casing which is integrally connected to the pump casing.
The motor actuation device can provide either for the simple direct supply of power to the motor or for a motor driving device, depending on the pump model chosen to meet the operating requirements.
To prevent the motor from being damaged by turning over with no load if the pump is not primed, in some cases there are sensors for detecting the level of the water in the well where the pump is located.
These sensors are adapted to detect the presence or absence of water at the level where they are arranged in the well.
Therefore, if the level of the water in the well does not reach the sensor, this is reported by the sensor and the motor is stopped, if it is running, or is prevented from starting if it is not running.
One drawback of this type of solution consists in the fact that the sensors can lose efficiency over time, by becoming gradually dirty during their active life and thus leading to incorrect reports which can cause damage to the motor if they do not report the absence of a water level in the well that is sufficient for pumping, or can prevent the operation of the pump if they do not detect the presence of water that is actually in contact with them.
The need is felt, therefore, to have devices which are reliable in detecting a condition of absence of sufficient pump priming and are at the same time efficient and durable.
Moreover, in order to make the performance of the pump suitable for the possible various different requirements that it is designed to meet, in order to save on actuation energy, it is currently known to provide an electronic device for driving the motor, particularly of the type known as an inverter.
This device is generally integrated in the pump actuation device, which is therefore external to the well and generally in proximity to the region of use of the water to be pumped.
One problem that is strongly felt in the field of making actuation units that are provided with motor control inverters consists in that the resistances and inductances of the cables for connecting the inverter to the motor impose a technical limitation on their length, which must be limited in order to ensure effective and efficient transmission of the driving signal.
Therefore, in practice an inverter that is arranged remotely from the motor cannot drive that motor effectively if the well is too deep or if the pump actuation device, which comprises the inverter, must be provided at a considerable distance from the motor.
In order to overcome this drawback, actuation units are currently known in which the motor is integrated with an inverter-based driving device.
However, the use of these devices presents some drawbacks, including the fact that they are structurally complex and expensive.
Moreover, they are not easy to maintain, and indeed if the motor or its driving device fails, it is necessary to replace the entire unit since they are integrated.